Your Postgres data on PythonAnywhere is fully protected against hardware failure. However, we do not automatically support rolling back to a point in time. If you want protection from accidental changes, you can set up a scheduled task to regularly back your data up to a file, which you can re-load into Postgres at a later date.
Here's an example of a command that can dump a particular database called "mydb":
pg_dump --host=HOSTNAME --port=PORT --username=super --format=c --file=pgbackup`date +%F-%H%M`.dump mydb
You'll want to experiment with
pg_restore until you have a backup command which you have confidence in -- remember, an untested backup procedure isn't a backup procedure at all!